| Under controlled temperature condition,the ultrastrnctural and physiological effects of cold stress on seedling leaves and roots of Eriobotrya japonica Lindl.were studied.The results showed as follows:1 The effect of cold stress on ultrastructure in E.japonica Lindl.Under 5℃,3℃cold stress,chloroplast,line plastochondria,vacuole cell organs and so on of loquat seedling leaf can maintain the basic structure and function,the cytoplasma membrane and the tonoplast are complete,with no burst phenomenon occurrence.The double-decked membrane structure of the chloroplast and the line plastochondria were still clearly discernible.It replied that the loquat seedling could adapt to 5℃,3℃cold sress.In the short time the freezeing injury is small or there is no freeze injury phenomenon.But there was a freeze injury in loquat seedling after a long time.Under -3℃,-5℃cold stress,12 hours' cold stress presents the cytoplasma membrane to burst,the chloroplast for disintegrates completely,the line plastochondria membrane structure loses and crista vanishes.These explained that under -3℃,-5℃cold stress loquat seedling receives a more serious freeze injury and it is irreversible and very difficult to restore again to the normal state.Under 5℃,3℃cold stress,the root system cytoplasma membrane was perfect, the membrane system structure was clear;the line plastochondria double-decked membrane structure was still clearly discernible,crista's structure was complete, internal structure had no too sweeping change.The vacuole monolayer membrane had not received the harm.The root system under 0℃the coercion,the primary protoplasmic membrane already received the destruction and becomes slurred, tonoplast structure shrinkage.Under -3℃,-5℃cold stress,the root system primary protoplasmic membrane,the fluid amnion receives the heavy damage,the protoplast concentration was a group and very difficult to restore again to the cell normal structure condition.The above phenomenon showed that the root system receives the freeze injury in the sub-zero temperature,it also indicated that the root system could't endure -3℃low temperature.Ultrastructure's change had the close relevance to the low temperature coercion signal sensitive degree.The identical temperature different time to the cell organ damage was different and the identical temperature was different to the different organ harm.The above conclusion showed that the root system was more sensitive to the low temperature.2 The effect of cold stress on physiological metabolism in E.japonica Lindl.The loquat seedling leaf blade under 5℃,3℃,0℃cold stress,PMP,the MDA content increased at first and reduced later,SOD,CAT and POD activeness as too and they had maintain the high level.The proline,the protein content increase at first and reducd later,and maintain high density.It indicated that the loquat under 5℃,3℃,0℃low temperature had certain adaptiveness.Under -3℃,-5℃cold stress PMP and MDA's content increased at first and reduced later,protective enzyme activity was suppressed. The proline and the protein's content were high,but under -5℃cold stress PMP and MDA's content increases large scale,protective enzyme activity was under serious suppression.Under 5℃,3℃,0℃,-3℃,-5℃low temperature,C/N ratio had sharp growth at first and droped later,this indicated that the ability of the root system absorbing coercion N droped and caused its upward transportation's N source dropping.But it droped later,this also showed that the aerial-part photosynthesis drops after cold stress,,at lasr the consumption increased.The loquat seedling leaf bladed under 5℃,3℃,0℃cold stress,PMP,the MDA content increased at first and reduced later,SOD,CAT and POD activeness as too and they had maintained the high level.The proline,the protein content increased at first and reduced later,and maintained high density.It indicates that the loquat under 5℃,3℃,0℃cold stress has certain adaptiveness.Under -3℃,-5℃cold stress PMP and MDA's content increase at first and reduce later,protective enzyme activity is suppressed.The proline and the protein's contents are increased;under 5℃,3℃,0℃,-3℃,-5℃cold stress,C/N ratio droped,but ground-part root system's C/N ratio assumed the declining trend,this indicated that the photosynthesis of ground-part reduced,the root was under cold stress,.The ability of transporting N source was blocked,C/N ratio assumed to drop compares to CK.The results of this thesis provided theoratical reference for climatic factors of cultivation and cultivated area,and had important theoratical and practical significance in fruit production... |
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